I created a (trial) azure account purely for the purposes of using oauth2 for signing into Microsoft 365 email accounts.
With this I have managed to get oauth2 to work (for IMAP and SMTP), for the email address of a user that I created in that azure account.
However it will not work for an email address created in someone else’s azure account for which I know the username and password.
When trying that address I’m also told that I have to add that email address as an external user.
When I do that it, OAuth2 access is granted but there’s no authentication for IMAP or SMTP.

I created a (trial) azure account purely for the purposes of using oauth2 for signing into Microsoft 365 email accounts.
With this I have managed to get oauth2 to work (for IMAP and SMTP), for the email address of a user that I created in that azure account.
However it will not work for an email address created in someone else’s azure account for which I know the username and password.
When trying that address I’m also told that I have to add that email address as an external user.
When I do that it makes no difference, ouath2 still fails.

Below is my $provider object:
Using this library